JPH06154762A - Method and device for separating ultrafine particles in muddy water treatment plant for excavating ground - Google Patents

Abstract

PURPOSE:To provide a separating device incorporated in a muddy water treatment plant at a working site of a continuous underground wall or the like and carry out consistently, continuously and simply the separation of ultrafine particles in the muddy water out of the muddly water in an efficient manner by the electrophoresis phenomenon and remove aggregates of ulfrafine particles off electrodes. CONSTITUTION:A plurality of electrode panel elements 4 are disposed in a water tank 1 filled with muddy water, and direct current voltage is applied between electrode panel elements 4 facing each other in the muddy water to aggregate ultrafine particles in the muddy water on the surfaces of elements as positive electrodes by the electrophoresis phenomenon. The application polarity of direct current voltage is turned over as the aggregates stuck to the elements grow larger, and the elements to which the aggregates are adhering are converted from the positive to negative electrode to drop the aggregates off the surfaces of the elements and precipitate them down on the bottom of the water tank 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of excavating the ground by using mud as a stable liquid such as a continuous underground wall method, a cast-in-place pile method, and a mud shield method. More particularly, the present invention relates to a method and a device for separating ultrafine particles contained in colloidal form in mud water after primary treatment.

[0002]

2. Description of the Related Art As a method for excavating the ground, there is known a mud construction method for advancing the excavation while the excavation hole is filled with mud in order to maintain the stability of the excavation hole wall. In this type of construction method, muddy water is treated and circulated in a plant attached to the construction site. The treatment targets of this plant are separation of excavated soil discharged along with circulating mud, treatment of surplus mud and deteriorated waste mud.

The state of mud water varies depending on the type and amount of excavated soil, type of stabilizing liquid material (bentonite, CMC, polymer agent, dispersant, etc.). The target of treatment is a wide range from colloidal particles to gravel, and generally the treatment process is divided into three stages. In the primary treatment, coarse solids in mud water are separated and removed by a method such as natural precipitation, forced precipitation and centrifugation. Generally, the primary treatment separates gravel, sand, and clay / silt lumps having a particle size of 74 μm or more. In the secondary treatment, clay / silt having a particle size of 74 μm or less is separated and removed from the separated water subjected to the primary treatment. In the tertiary treatment, the pH of the secondary treated water is adjusted and the treated water is discharged or reused as construction water.

In a typical conventional secondary treatment, a method is used in which a flocculant is added to and mixed with mud water, and flocculated flocs are forcedly dehydrated. Various types of dewatering devices have been developed, and pressure dewatering machines such as filter presses and roll presses are commonly used. However, this type of conventional method has a problem that it is not possible to sufficiently separate the ultrafine particles of the clay component dispersed in colloidal form in the muddy water. As a means for solving this problem, the present applicants have previously developed a method for separating ultrafine particles as disclosed in JP-A-4-254690.

In this method, two electrode plates are placed opposite to each other in a water tank containing mud water after the primary treatment, a DC voltage is applied to both electrodes, and ultrafine particles in the mud water are electrophoresed to the positive electrode side. To agglomerate. As a result, ultrafine particles in the muddy water are separated and clear water is obtained.

[0006]

The effectiveness of the above-mentioned method for treating mud water applying the electrophoretic phenomenon was clearly confirmed at the laboratory level, but the speed required at the actual construction site was confirmed. However, it was not sufficient to efficiently separate ultrafine particles. In particular, since a means for easily removing the aggregate of ultrafine particles adhering to the electrode from the electrode has not been developed, it has been impossible to efficiently process a large amount of muddy water that is generated one after another.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to be incorporated in a muddy water treatment plant at a construction site such as a continuous underground wall to efficiently remove ultrafine particles in muddy water by an electrophoretic phenomenon. It is to make it possible to consistently and easily separate well and to remove the agglomerates of ultrafine particles adhering to the electrode from the electrode.

[0008]

In the present invention, therefore, a plurality of electrode panel elements are arranged in a water tank containing muddy water, and a DC voltage is applied between the electrode panel elements facing each other in muddy water. Of the ultrafine particles are aggregated on the surface of the element, which is a positive electrode by an electrophoretic phenomenon, and the applied polarity of the DC voltage is reversed after the agglomerates adhered to the element grow large, and the agglomerates adhered. By changing the element from a positive electrode to a negative electrode, the agglomerate was dropped from the surface of the element and settled on the bottom of the water tank.

Further, the ultrafine particle separating apparatus for carrying out the above method is provided with a water tank to which mud water to be treated is supplied, a plurality of electrode panel elements arranged in the water tank, and the electrodes facing each other. A direct current power source for applying a direct current voltage between the panel elements, a switching means for switching the polarity of the direct current voltage applied from the direct current power source between the electrode panel elements, and a precipitate at the bottom of the water tank outside the water tank. And means for discharging to.

[0010]

The principle of separation is that the ultrafine particles in the muddy water are attracted to the positive electrode element side by the electrophoretic phenomenon and aggregated, which is the same as the above-mentioned prior art. When a considerable amount of ultrafine particles adhere to the positive electrode element as an aggregate, the effect of further attracting and aggregating the ultrafine particles in the muddy water is significantly reduced. Therefore, when the polarity of the DC voltage applied to the electrode panel element is reversed, the direction of the electric field is reversed, so that the agglomerate attached to the element switched from the positive electrode to the negative electrode remains in a clumped state. It will fall off and will settle on the bottom of the tank without being dispersed in muddy water. Therefore, the ultrafine particles are separated in the previous step and clear water does not become cloudy again. It is possible to easily discharge the agglomerated lumps that have formed into lumps and settled to the bottom to the outside of the water tank with the same configuration as that of the primary treatment device.

When a DC voltage is applied to the opposing electrode panel element in the muddy water, an electrolysis reaction occurs and hydrogen gas is generated from the negative electrode side. This gas generation is caused by the agglomerates attached to the element. It produces a peeling effect that causes the particles to float up from the electrode surface, so that the agglomerates can be dropped from the element very well.

[0012]

1 to 4 show the construction of a separating apparatus according to an embodiment of the present invention. Reference numeral 1 is a rectangular flat mud tank with an open top surface, and an inlet 2 for supplying mud water into the tank is provided at one end side in the longitudinal direction, and the treated water is discharged at the other end side. An exit 3 is provided for In the muddy water tank 1, 14 electrode panel elements 4 are arranged by a support mechanism described below. The electrode panel elements 4 are vertically inserted in the tank, are orthogonal to the longitudinal direction of the muddy water tank 1, and are arranged substantially in parallel at regular intervals.

The electrode panel element 4 is made of expanded metal cut into a substantially square shape, and is attached to the panel frame 5. On the upper part of each panel frame 5, an individual bar 6 projecting long on both sides is attached, and the individual bar 6 supports the entire base element 7
Is attached to. The support base rail 7 is set so as to be placed on the upper edge of the muddy water tank 1. The support rails 7 are set so that the individual rails 6 are hung, the panel frame 5 is suspended below the individual rails 6, and the electrode panel element 4 is mounted in the frame of the panel frame 5. There is.

The support base rails 7 are made of an insulating material so that the fifteen electrode panel elements 4 arranged in the muddy water tank 1 are individually electrically insulated except for the connection by the wiring mechanism described below. Or support base bar 7
Means such as interposing an insulating material at the contact portion of the individual crosspiece 6 are taken. In this manner, each electrode panel element 4 is individually insulated, and each element 4 and the DC power source 8 are connected by the power distribution cable 9 via the polarity switcher 10.

The bottom of the muddy water tank 1 has a valley shape, and the screw conveyor 11 is arranged along the bottom. The screw conveyor 11 is driven by a motor 15 and conveys the solid matter deposited on the bottom of the muddy water tank 1 from left to right in FIG. The right end portion of the screw conveyor 11 projects laterally of the muddy water tank 1 in a pipe shape, and a vertical screw conveyor 12 is connected to the portion and is arranged substantially vertically. The vertical screw conveyor 12 is driven by a motor 13 and conveys the precipitate conveyed by the screw conveyor 11 upward. Vertical conveyor 12
Is set higher than the water surface of the muddy water tank 1, and the precipitate conveyed by the vertical conveyor 12 is separated from the muddy water and drops from the carry-out outlet 12a onto the belt conveyor 14 immediately below the muddy water. Transported to the deposition site.

The operation and usage of the separating device configured as described above will be described. This separation device serves as a secondary treatment means in a treatment plant for ground mud. As described above, muddy water from which gravel, sand, and coarse particles such as clay / silt lumps have been separated and removed by the primary treatment is supplied from the inlet 2 to the muddy water tank 1. The secondary treatment in the muddy water tank 1 may be a batch type or a continuous flow type. In the case of the batch system, the DC power supply 8 energizes the electrode panel element group 4 in a state where the tank is filled with the muddy water after the primary treatment. Then, an electrophoretic phenomenon occurs in the space between the electrode panel elements 4 facing each other in the muddy water tank 1 as a positive electrode and a negative electrode, and ultrafine particles such as clay and silt contained in colloidal form in the muddy water. It moves toward the positive electrode element 4 side and is adsorbed, and an aggregate of ultrafine particles grows on the surface of the electrode panel element 4 made of expanded metal. Therefore, the muddy water in the tank 1 gradually becomes clear.

When current is continuously applied with a certain applied polarity, the agglomerates attached to and grown on the positive electrode element become considerably large and thick, and further agglomeration cannot be performed efficiently. At an appropriate point before such a case, the polarity switching device 10 reverses the polarity of the DC voltage applied to the electrode panel element 4 group, and the element in which the ultrafine particles are aggregated is switched to the negative electrode.
The element facing this is switched to the positive electrode.
Then, the agglomerated lumps adhering to the element and growing, fall out of the element as lumps and settle on the bottom of the muddy water tank 1. Also, from this time, ultrafine particles newly start to aggregate on the surface of the element that has become the positive electrode. That is, every other half of the electrode panel element 4 group alternately becomes positive electrodes, and in the process in which the ultrafine particles are aggregated in one group, the aggregates that have adhered and grown up to immediately before in the other group fall off. It will be. This operation is alternately repeated at appropriate intervals.

The treated water, which is sufficiently clear by the above treatment, is discharged from the outlet 3 at an appropriate time. When the treatment is carried out by the continuous flow method, the muddy water is supplied from the inlet 2 to the outlet 3 very slowly so that the muddy water before the treatment and the water after the treatment gradually flow without being mixed with each other.

When a certain amount of solid matter (the above-mentioned aggregate) is accumulated at the bottom of the muddy water tank 1, the screw conveyor 11, the vertical screw conveyor 12, and the belt conveyor 14 are driven to move the precipitate to the outside of the tank. Discharge. here,
If the screw conveyor 12 is applied negatively, it is possible to suppress the attachment of the agglomerates of ultrafine particles, and it is easy to remove the attached agglomerates.

The electrode panel element 4 preferably has a lattice-like or mesh-like structure as described in the embodiment. Even if a large number of electrode panel elements are arranged in a muddy water tank, if the elements have a grid or mesh structure, the fluidity of water in the tank is not significantly hindered, the electrode surface area is large, and the electrode surface Agglomerates of ultra-fine particles that aggregate in a stable manner adhere to each other. Suitable materials for the electrode panel element include gratings and punching metals in addition to the expanded metal described above.

In the embodiment of the separating apparatus described above, the muddy water tank is integrally provided with the screw conveyor for discharging the sediment, but the separating method of the present invention is effective even if it is not such an apparatus form. Can be carried out. The agglomerates attached by switching the applied voltage immediately fall off from the element, so after that, the electrode panel element 4 group is integrally moved to another muddy water tank, and the muddy water in the water tank is treated. The discharge treatment of the precipitate in the water tank until then may be performed separately.

[0022]

As described in detail above, according to the present invention, it is possible to efficiently separate the ultrafine particles in the mud water on the electrode by the electrophoretic phenomenon, and to polarize the voltage applied to the electrode. It is possible to quickly remove the agglomerates of ultrafine particles adhering to the electrodes by a very simple means of switching. That is, it is possible to consistently and extremely efficiently aggregate the ultrafine particles in the muddy water to the electrode and drop the aggregated mass from the electrode as it is. It is possible to realize a muddy water treatment plant that treats the muddy water.

[Brief description of drawings]

FIG. 1 is a plan view of a separation device according to an embodiment of the present invention.

FIG. 2 is a front view of the above-mentioned embodiment apparatus.

FIG. 3 is a side view of the apparatus according to the above embodiment.

FIG. 4 is a detailed view of an electrode panel element portion in the device of the above embodiment.

[Explanation of symbols]

 1 Muddy Water Tank 2 Inlet 3 Outlet 4 Electrode Panel Element 5 Panel Frame 6 Individual Rail 7 Support Base Rail 8 DC Power Supply 9 Distribution Cable 10 Polarity Switch 11 Screw Conveyor 12 Vertical Screw Conveyor 13 Motor 14 Belt Conveyor 15 Motor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaaki Yoshizaki 2-3 Kandaji-cho, Chiyoda-ku, Tokyo Obayashi Corporation Tokyo Head Office

Claims (2)

[Claims] 1. A plurality of electrode panel elements are arranged in a water tank containing mud water, a DC voltage is applied between the electrode panel elements facing each other in the mud water, and ultrafine particles in the mud water are corrected by an electrophoretic phenomenon. Aggregate on the surface of the element that is an electrode, reverse the applied polarity of the DC voltage after the agglomerate attached to the element grows large,
By changing the element to which the agglomerate is attached from a positive electrode to a negative electrode, the agglomerate is dropped from the surface of the element and settles on the bottom of the water tank, ultrafine particles in a mud treatment plant for ground excavation. Separation method. 2. A DC tank for supplying muddy water to be treated, a plurality of electrode panel elements arranged in the tank, and a DC power source for applying a DC voltage between the adjacent electrode panel elements. And switching means for switching the polarity of the DC voltage applied from the DC power supply between the electrode panel elements, and means for discharging the precipitate at the bottom of the water tank to the outside of the water tank. Separation device for ultra-fine particles in a mud treatment plant for ground excavation.